1. Field of the Invention
The invention relates to a method of error correction, and more particularly relates to a method of error correction for either burst or random errors wherein detection of such errors is greatly enhanced and erroneous correction is significantly reduced.
2. Description of the Prior Art
In the transmission of data, various electrical and electromagnetic disturbances can occur that degrade the quality of the transmitted data. That is, the disturbances create errors in the data. One type of error occurs when a number of bits in series are dropped from and/or added to the transmission of data. Such an error is commonly referred to as a burst error. Applicant of the present invention has previously proposed a cross-interleave technique which substantially maintains the original quality of the transmitted data when burst errors occur.
In the cross-interleave technique one word contained in each pulse code modulated (PCM) data series in a plurality of channels in a first arrangement state is supplied to a first error correcting encoder so as to produce a first series of check words. The first series of check words and the PCM data series in the plurality of channels are then arranged in a second arrangement state such that one word contained therein is supplied to a second error correcting encoder to provide a second series of check words. That is, a double interleave (rearrangements of check word and data) technique is performed by word unit. Therefore, the interleave technique provides dispersion and transmission of check words and PCM data contained in a common error correcting block. Such an encoding technique provides, after decoding of the data, a reduction in the number of error words in the plurality of words contained in the common error correcting block. In particular, when burst errors occur in the transmission of data, such burst errors will be dispersed due to the interleaving technique. If the interleave technique is performed twice, the first and second check words, respectively, constitute independent error correcting blocks so that errors not corrected by one series of check words, can be corrected by the other series of check words. Thus the error correcting ability is significantly improved.
However, in such a cross-interleave technique if only one bit is erroneous in a word containing, for example, eight bits, the entire word is treated as erroneous, so that for received data which contains relatively many random errors, far too many data bits are labeled as erroneous resulting in a limited error correcting ability.
Therefore, it is desirable to combine an error correcting code, such as a kind of b-adjacent code, having a high error correcting ability that corrects K words within one block, for instance, up to two word errors, and when the error location is known, M words, for instance, up to four word errors, with the foregoing cross or multi-interleave technique. When only one word error is intended to be corrected, the above error correcting code includes a feature which significantly simplifies construction of the decoder.
Additionally, when a second error correcting block is decoded at the first decoding stage and arranged once again in the first arrangement state so as to decode a first error correcting block at the next stage of decoding, the existence or presence of an error in the data therein may be identified as the absence of error, that is, as non-detection of an error or, four word errors may be detected as only one word error and thereby cause an erroneous correction. Such non-detection or erroneous correction can cause additional non-detection of errors or erroneous corrections during the next stage of decoding and thereby significantly increase the likelihood that such errors will occur. Moreover, as the number of words that require correction increases, the probability of non-detection of errors and erroneous correction is increased. Furthermore, if transmitted audio PCM signals are erroneously corrected upon transmission thereof, abnormal and undesirable sound signals are reproduced.